In a groundbreaking study published in the esteemed journal Current Biology, scientists have unravelled the extraordinary mechanics behind the distinctive whinny of horses—a sound that intriguingly combines high and low frequency components. Unlike typical large mammals that emit low-pitched vocalizations due to their sizeable larynx, horses defy this norm by generating a complex acoustic signal encompassing two simultaneous fundamental frequencies. This dual-tone phenomenon, known as biphonation, had mystified researchers until now, who have revealed that horses produce the high-frequency element using a unique aerodynamic whistle generated within the larynx itself, while the low-frequency sound arises from traditional vocal fold vibrations.
The research team, led by Elodie Briefer at the University of Copenhagen, used a combination of anatomical studies, acoustic analyses, and innovative physiological experiments to decode this vocal enigma. Their investigations demonstrate that the high-frequency component of the horse’s whinny originates from a turbulent airstream—a whistle—created in the laryngeal airway, distinct from the vocal fold oscillations responsible for the lower frequencies. This dual sound production mechanism has never before been documented in large mammals, positioning horses as singular in their vocal abilities among the animal kingdom.
Horses typically produce sound through the vibration of their vocal folds, akin to how humans sing or cats meow. However, the acoustic richness of their whinny features a simultaneous high-pitched whistle that adds a surprising layer of complexity. The researchers hypothesize that such an adaptation allows horses to communicate a richer array of emotional states and messages by conveying multiple, independent acoustic signals concurrently, enhancing social communication within herds.
To probe the source of the high-frequency whistle, the scientists employed excised larynx experiments on post-mortem horse specimens. By channeling air through these isolated larynxes, they meticulously observed sound production in controlled laboratory settings. They further manipulated the composition of the airstream, alternating between air and helium to capitalize on the differing speed of sound in these gases. As predicted by aerodynamic principles, the whistle frequency increased with helium airflow, while vocal fold vibration frequencies remained steady, conclusively isolating the whistle as a distinct aerodynamic mechanism.
This meticulous experimental design provided the key evidence confirming that the high-frequency sounds in horse whinnies are produced by a laryngeal whistle, an acoustic phenomenon previously attributed only to certain small rodents like mice and rats. Notably, this makes horses the first large mammal—and uniquely, the only known animal—to produce this whistle simultaneously with vocal fold vibration, underscoring an unprecedented evolutionary vocal innovation.
The discovery challenges traditional assumptions about mammalian vocal anatomy and acoustic capacity, emphasizing the need to rethink how body size correlates with vocal pitch. Larger mammals generally produce lower sounds because their large larynges generate slower vocal fold vibrations. Horses break this mold by combining low-frequency vocal fold sounds with a high-frequency aerodynamic whistle, thereby expanding the acoustic space they can occupy.
Examining comparative species, the research team noted that Przewalski’s horses, the wild relatives of domestic horses, share this biphonation ability, whereas more distantly related equids such as donkeys and zebras do not exhibit the same high-frequency component. This points to a unique evolutionary pathway in horses, equipping them with a broader and more expressive vocal repertoire unmatched in related species.
The complexity of horse vocalizations may have played a critical role in their social interactions, allowing nuanced communication that can convey emotions like distress, excitement, or aggression across different acoustic channels simultaneously. The ability to layer sounds in this manner could provide an evolutionary advantage in maintaining herd cohesion and coordinating group behaviors, vital for survival in natural environments.
This research also contributes to expanding the field of bioacoustics, offering new insights into how animals harness diverse physical mechanisms to generate sound. The concept of aerodynamic whistles coexisting with vocal fold vibrations broadens the scope of vocal production theories and opens new avenues for investigating communication across species.
David Reby of the University of Lyon/Saint-Etienne, a co-author on the study, highlights that understanding the emergence of biphonation in horses brings us closer to deciphering the origins of mammalian vocal diversity. It underscores how evolutionary pressures can lead to novel vocal adaptations, shaping communication complexity and social behaviors in the animal kingdom.
The study received generous funding from the Swiss National Science Foundation, the Austrian Science Fund, and the Institut Universitaire de France, reflecting its significance and the collaborative effort spanning veterinary medicine, acoustic physics, and evolutionary biology.
As more is uncovered about the biomechanical and evolutionary facets of horse vocalizations, this research advances our grasp of animal communication and holds promise for enhancing human understanding of voice production. The detailed insight into how horses create their iconic whinnies enriches not only biological knowledge but also deepens our appreciation for these majestic creatures and their remarkable capacity for expression.
Subject of Research: Animals
Article Title: The high fundamental frequency in horse whinnies is generated by an aerodynamic whistle
News Publication Date: 23-Feb-2026
Web References: http://www.cell.com/current-biology
References: Lefèvre et al., Current Biology, 2026
Image Credits: Elodie Briefer
Keywords: Animal communication, Bioacoustics, Animal sounds, Vocalization, Larynx
